U.S. patent application number 15/112924 was filed with the patent office on 2016-11-17 for rigid polyurethane foam having a small cell size.
This patent application is currently assigned to Dow Global Technologies LLC. The applicant listed for this patent is DOW GLOBAL TECHNOLOGIES LLC, Rohm and Haas Company. Invention is credited to Luigi Bertucelli, Ning Chai, Cheng Chen, Jing Chen, Stephane Costeux, Hong Fei Guo, Dachao Li, Wei Liu, Vanni Parenti, Billy G. Smith, Beilei Wang, Yige Yin.
Application Number | 20160333160 15/112924 |
Document ID | / |
Family ID | 53680599 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160333160 |
Kind Code |
A1 |
Bertucelli; Luigi ; et
al. |
November 17, 2016 |
RIGID POLYURETHANE FOAM HAVING A SMALL CELL SIZE
Abstract
A rigid polyurethane (PU) foam having a number average cell size
of no greater than 10
Inventors: |
Bertucelli; Luigi;
(Correggio, IT) ; Parenti; Vanni; (Correggio,
IT) ; Li; Dachao; (Columbus, OH) ; Liu;
Wei; (Shanghai, CN) ; Chai; Ning; (Pittsburg,
CA) ; Wang; Beilei; (Shanghai, CN) ; Chen;
Cheng; (Shanghai, CN) ; Guo; Hong Fei;
(Shanghai, CN) ; Chen; Jing; (Shanghai, CN)
; Yin; Yige; (Shanghai, CN) ; Costeux;
Stephane; (Midland, MI) ; Smith; Billy G.;
(Brazoria, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOW GLOBAL TECHNOLOGIES LLC
Rohm and Haas Company |
Midland
Philadelphia |
MI
PA |
US
US |
|
|
Assignee: |
Dow Global Technologies LLC
Midland
MI
Rohm and Haas Company
Philadelphia
PA
|
Family ID: |
53680599 |
Appl. No.: |
15/112924 |
Filed: |
January 23, 2014 |
PCT Filed: |
January 23, 2014 |
PCT NO: |
PCT/CN2014/071239 |
371 Date: |
July 20, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08G 18/4816 20130101;
C08G 18/1816 20130101; B29C 44/10 20130101; C08G 18/7671 20130101;
C08G 2101/0025 20130101; C08J 2375/08 20130101; C08G 18/2036
20130101; C08G 18/4829 20130101; C08J 2203/08 20130101; C08J
2205/10 20130101; C08J 2201/022 20130101; B29K 2075/00 20130101;
C08J 2203/06 20130101; C08G 18/48 20130101; C08G 18/163 20130101;
C08J 2205/05 20130101; C08J 2205/044 20130101; C08J 9/122 20130101;
B29C 44/348 20130101; C08G 18/225 20130101; C08G 18/1808 20130101;
C08G 18/7664 20130101 |
International
Class: |
C08J 9/12 20060101
C08J009/12; C08G 18/48 20060101 C08G018/48; C08G 18/18 20060101
C08G018/18; C08G 18/20 20060101 C08G018/20; B29C 44/10 20060101
B29C044/10; C08G 18/76 20060101 C08G018/76 |
Claims
1. A method for preparing a rigid polyurethane foam, comprising:
using carbon dioxide to provide a pressure at a first predetermined
value on a polyol mixture that includes a polyol, a catalyst and a
surfactant; maintaining the pressure at the first predetermined
value for a first predetermined time; mixing an isocyanate with the
polyol mixture to form a polyurethane reaction mixture; optionally
maintaining the pressure on the polyurethane reaction mixture at
the first predetermined value for a second predetermined time;
increasing the pressure on the polyurethane reaction mixture from
the first predetermined value to a second predetermined value
greater than the first predetermined value; and releasing the
polyurethane reaction mixture at a predetermined depressurization
rate from the pressure after a third predetermined time to prepare
the rigid polyurethane foam, where the third predetermined time is
less than 30 minutes.
2. The method of claim 1, where the first predetermined value is
from 5 megapascal (MPa) to 10 MPa at a temperature of 40 degrees
Celsius (.degree. C.) to 80.degree. C.
3. The method of claim 2, where the first predetermined time is
from 30 seconds (s) to 300 s.
4. The method of claim 1, where the second predetermined value is
from greater than 10 MPa to 15 MPa at a temperature of 31.degree.
C. to 80.degree. C.
5. The method of claim 1, where using carbon dioxide to provide the
pressure at the first predetermined value on the polyol mixture
includes using carbon dioxide in a supercritical state to provide
the pressure at the first predetermined value on the polyol
mixture.
6. The method of claim 1, where optionally maintaining the pressure
on the polyurethane reaction mixture at the first predetermined
value for the second predetermined time increases a carbon dioxide
content of the polyurethane reaction mixture to a value of at least
20 weight percent based on the total weight of the polyol mixture
after the first predetermined time.
7. The method of claim 1, where the polyol mixture has a number
averaged functionality of at least 2 and an average hydroxyl value
of at least 100 mg KOH/g.
8. The method of claim 1, where the polyol is selected from the
group consisting of a polyether polyol, a polyester polyol or a
combination thereof.
9. The method of claim 1, where the isocyanate is selected from the
group consisting of an aliphatic isocyanate, a cycloaliphatic
isocyanate, an aromatic isocyanate, a polyisocyanate prepolymer or
a combination thereof.
10. The method of claim 1, where the predetermined depressurization
rate is at least 350 MPa/s.
11. The method of claim 1, where mixing the isocyanate with the
polyol mixture to form the polyurethane reaction mixture provides a
molar ratio of isocyanate groups to hydroxyl groups of greater than
1 to 1.
12. The method of claim 1, further including applying a vacuum to
the rigid polyurethane foam.
13. A rigid polyurethane foam formed by the method of claim 1.
14. The rigid polyurethane foam of claim 13, where the rigid
polyurethane foam has a number average cell size of no greater than
10 .mu.m.
15. The rigid polyurethane foam of claim 13, where the rigid
polyurethane foam has a crosslink density from 1.0 to 3.0 and a
weight average molecular weight (Mw) per cross-link from 300 to
900.
16. The rigid polyurethane foam of claim 13, where the rigid
polyurethane foam has a porosity of no less than 85 percent.
17. The rigid polyurethane foam of claim 13, where the rigid
polyurethane foam has an open cell volume content from 35 percent
(%) to 95% based on all the cells in the rigid PU foam.
18. An insulation panel formed with the rigid polyurethane foam of
claim 13.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to polyurethane
foam and more particularly to rigid polyurethane foam having a
small cell size.
BACKGROUND
[0002] Rigid polyurethane (PU) foam is widely used in appliance and
building industries due to its excellent thermal insulation
property. Using rigid PU foam with improved thermal insulation
performance is one objective for appliance manufacturers. It is
known that the thermal conductivity (Lambda, .lamda.) of rigid PU
foam is attributed to at least heat conduction through the gas
contained in the rigid PU foam (gas conductivity), conduction
through the solid structure of the rigid PU foam (solid
conductivity) and from the radiant heat transfer of the rigid PU
foam. In conventional rigid PU foams used for appliance, gas
conductivity accounts for about 60-70% of the total lambda value.
One conventional method to minimize gas conductivity is to use
certain types of blowing agents such as hydrochlorofluorocarbons
(HCFC, e.g., HCFC141b), hydrofluorocarbons (e.g. HFC245fa),
hydrofluoroolefines (HFOs), hydrocarbons (e.g. c-pentane), and
mixtures thereof in the production of the rigid PU foams. Some of
these gases, however, are known to have ozone depletion potential
(ODP) or global warming potential (GWP).
[0003] Another approach to minimize gas conductivity is to limit
the number of energy exchanging collisions between gas molecules in
the cells of the rigid PU foam. Minimizing the number of collisions
between gas molecules in the cells can effectively reduce gas
conductivity without the use of HCFC, HFC, HFOs or hydrocarbons. To
achieve this result the size of the cells of the rigid PU foam
needs to be close to or smaller than the mean free path of gas
molecules between collisions. This is known as the "Knudsen effect"
and can be achieved either by reducing the size of the cells, by
reducing the gas pressure inside the cells, or both.
[0004] Foaming methods used with rigid PU foams do not, however,
readily achieve cell size below about 180 micrometer (.mu.m). For
such foams, strong vacuum needs to be applied (<1 mbar, often
<0.1 mbar) to achieve conditions under which the Knudsen effect
becomes significant. Thus, there is a need for rigid PU foams
having small cells that can achieve low thermal conductivity values
(e.g., less than 18 mW/m-K) without the need of very strong vacuum
or for the use of gases that have ODP or GWP.
SUMMARY
[0005] The present disclosure provides a rigid polyurethane (PU)
foam having a cell size small enough to possibly achieve low
thermal conductivity values (e.g., lower than 18 mW/m-K and
preferably lower than 16 mW/m-K) without the need of a strong
vacuum or for the use of gases that could contribute to GWP or VOC.
The rigid PU foam is prepared by a method that includes using
carbon dioxide (CO.sub.2) to provide a pressure at a first
predetermined value on a polyol mixture that includes a polyol, a
catalyst and a surfactant; maintaining the pressure at the first
predetermined value for a first predetermined time; mixing an
isocyanate with the polyol mixture to form a polyurethane reaction
mixture; optionally maintaining the pressure on the polyurethane
reaction mixture at the first predetermined value for a second
predetermined time; increasing the pressure on the polyurethane
reaction mixture from the first predetermined value to a second
predetermined value greater than the first predetermined value; and
releasing the polyurethane reaction mixture at a predetermined
depressurization rate from the pressure after a third predetermined
time to prepare the rigid PU foam, where the third predetermined
time is less than 30 minutes.
[0006] Maintaining the pressure at the first predetermined value
using CO.sub.2 for the first predetermined time allows for the
CO.sub.2 content of the polyol mixture to increase. For example,
optionally maintaining the pressure on the polyurethane reaction
mixture at the first predetermined value for the second
predetermined time using CO.sub.2 increases a carbon dioxide
content of the polyurethane reaction mixture to a value of at least
20 weight percent (up to the saturation value) based on the total
weight of the polyol mixture after the first predetermined
time.
[0007] The CO.sub.2 used to provide, maintain and/or increase the
pressure can include using CO.sub.2 in one of a subcritical or a
supercritical state, as discussed herein. For example, the first
predetermined value of the pressure can be from 5 to 10 MPa at a
temperature of 40.degree. C. to 80.degree. C. Specific combinations
of these temperatures and pressures for the CO.sub.2 allow the
CO.sub.2 used in providing and/or in maintaining the pressure at
the first predetermined value to be in either a subcritical or a
supercritical state. In an additional example, the second
predetermined value of the pressure can be from greater than 10 MPa
to 15 MPa at a temperature of 40.degree. C. to 80.degree. C. This
combination of temperatures and pressures for the CO.sub.2 allow
the CO.sub.2 used in increasing the pressure on the polyurethane
reaction mixture from the first predetermined value to the second
predetermined value greater than the first predetermined value to
be in a supercritical state.
[0008] Each polyol used in the polyol mixture can be selected from
the group consisting of a polyether polyol, a polyester polyol or a
combination thereof. The isocyanate can be selected from the group
consisting of an aliphatic isocyanate, a cycloaliphatic isocyanate,
an aromatic isocyanate, a polyisocyanate prepolymer or a
combination thereof. Mixing the isocyanate with the polyol mixture
to form the polyurethane reaction mixture can provide a molar ratio
of isocyanate groups to hydroxyl groups of greater than 1 to 1.
[0009] Releasing the polyurethane reaction mixture at the
predetermined depressurization rate from the pressure after the
third predetermined time to prepare the rigid PU foam can
preferably be done at the predetermined depressurization rate of at
least 350 MPa/s. Other predetermined depressurization rates are
possible (e.g., 350 to 400 MPa/s).
[0010] The method of the present disclosure can be performed in a
single vessel in a batch process. Alternatively, the method of the
present disclosure can be performed in two or more vessels. When
two or more vessels are used, the method can be done in a batch, a
semi-batch or a continuous process, as discussed herein.
[0011] The rigid PU foam produced by the method of the present
disclosure can have a number average cell size of no greater than
10 micrometer (.mu.m). The rigid PU foam of the present disclosure
can also have a crosslink density from 1.0 to 3.0 and a weight
average molecular weight (Mw) per cross-link from 300 to 900.
DETAILED DESCRIPTION
Definitions
[0012] As used herein "rigid polyurethane (PU) foam" is a PU foam
that have an elastic region in which strain is nearly proportional
to stress; which when compressed beyond its yield point the cell
structure is crushed; where the compressive strength values of 10
to 280 kPa (1.45-40.6 psi) can be obtained using rigid PU foams
having a density of at least 40 kg/m.sup.3. In addition, the
elastic modulus, shear strength, flexural strength, and tensile
strength all increase with density.
[0013] As used herein "number average cell size" "D" is calculated
using the following equation:
D = d i n i n i ##EQU00001##
where n.sub.i is the number of cells with a perimeter-equivalent
diameter of d.sub.i.
[0014] The rigid PU foam can be characterized in having a
calculated molecular weight between crosslinks. The calculated
molecular weight between crosslinks (Mc) takes into account the
functionality (number of isocyanate or isocyanate-reactive groups
per molecular) and equivalent weight of those polyisocyanate
compounds and of those isocyanate-reactive compounds together with
the isocyanate index, as follows:
Crosslink Density = 1000 / Mc ##EQU00002## Mc = Wpol + Wiso Wpol (
Fpol - 2 ) Epol .times. Fpol + Wiso , stoich ( Fiso - 2 ) Eiso
.times. Fiso + Wiso , exc ( Fiso - 1 ) Eiso ( Fiso + 1 )
##EQU00002.2##
[0015] Wpol is the weight of the polyol; Wiso is the weight of the
isocyanate; Wiso,stoich is the weight of the stoichiometric amount
of isocyanate in grams; Wiso,exc is the weight of the isocyanate
exceeding the stoichiometric amount; iso is isocyanate; pol is
polyol; F is the numerical average functionality of the components;
and E is the equivalent weight of the components.
[0016] As used herein, "porosity" is defined as a measure of the
void (i.e., "empty") spaces in a material, and is a fraction of the
volume of voids over the total volume, between 0-1, or as a
percentage between 0-100%. Porosity is determined using ASTM
D792-00 or EN ISO 845.
[0017] As used herein, carbon dioxide "saturation" is defined as a
weight percent of CO.sub.2 that has been dissolved in a solution
(e.g., the polyol mixture and/or the polyurethane reaction mixture)
compared to the saturation equilibrium level, and is measured using
a magnetic suspension balance.
[0018] As used herein, an "open cell" of the rigid PU foam is
defined as the cell which is not completely closed and directly or
indirectly interconnecting with other cells, and is measured
according to ASTM D2856.
[0019] As used herein, a "closed cell" of the rigid PU foam is
defined as the cell which is completely closed and non-connecting
with any other cells, and is measured according to ASTM D2856.
[0020] As used herein, carbon dioxide in a "subcritical state" is
defined as carbon dioxide with a pressure of no less than 5
megapascal (MPa) and no larger than the critical pressure of 7.3
MPa for a temperature of at least 0.degree. C.
[0021] As used herein, carbon dioxide in a "supercritical state" is
defined as CO.sub.2 under a pressure of at least the critical
pressure of 7.3 MPa and a temperature of at least the critical
temperature of 31.3.degree. C.
[0022] Embodiments of the present disclosure can provide for a
rigid polyurethane (PU) foam having a number average cell size of
no greater than 10 micrometer (.mu.m) and a porosity of no less
than 85%. Embodiments of the present disclosure can also provide
for a method of producing the rigid PU foam having a number average
cell size of no greater than 10 .mu.m and a porosity of no less
than 85%. The method of producing the rigid PU foam uses carbon
dioxide (CO.sub.2) as the blowing agent. Unlike certain other
blowing agents, such as chlorofluorocarbons, or fluorocarbons,
CO.sub.2 is an environmentally sustainable physical blowing agent
with zero ODP and negligible GWP.
[0023] One difficulty in using CO.sub.2 as the blowing agent in
making the rigid PU foam is the significant influence CO.sub.2 can
have on PU reaction kinetics. For example, PU foaming methods that
use high concentrations of CO.sub.2 in a single step foaming
operation can slow down the PU reaction such that polymerization
and foaming cannot be effectively decoupled. This brings many
difficulties in process design and control. It also produces a PU
foam having a bi-modal cell size distribution, which is not
desirable. The present disclosure provides for a two-stage CO.sub.2
pressurization process, as discussed herein, that can provide a
rigid PU foam having what could be considered a unimodal cell size
distribution. The present disclosure also at least partially
decouples the polymerization and foaming processes that allows for
the molecular weight of the PU to build before forming the rigid PU
foam so that the cell size and porosity of the rigid PU foam can
achieve the number average cell size of no greater than 10 .mu.m
and a porosity no less than 85%.
[0024] Preferably, the number average cell size of the rigid PU
foam of the present disclosure is no greater than 10 .mu.m, which
would enable the Knudsen effect at pressures higher than 1 millibar
(mbar), or even higher than 10 mbar. Additionally, the method to
make the rigid PU foam of the present disclosure preferably uses
supercritical carbon dioxide (scCO.sub.2) as the blowing agent,
which can reduce cost and help protect the environment.
[0025] The method of the present disclosure includes a two-stage
CO.sub.2 pressurization process in forming the rigid PU foam. In
the first stage of the two-stage CO.sub.2 pressurization process
the method includes using CO.sub.2 to provide a pressure having a
first predetermined value on a polyol mixture. The polyol mixture
includes a polyol, a catalyst and a surfactant. The polyol mixture
can also include one or more additional compounds, as discussed
herein. The CO.sub.2 used to provide the pressure having a first
predetermined value on a polyol mixture can be in either a
subcritical state or a supercritical state. The pressure at the
first predetermined value is maintained for a first predetermined
time. Maintaining the pressure having the first predetermined value
on the polyol mixture can be done with CO.sub.2. For example,
CO.sub.2 can be supplied to a vessel (e.g., pumped into the vessel)
containing the polyol mixture in order to maintain the pressure at
the first predetermined value. Alternatively, the volume of a
head-space containing the CO.sub.2 above the polyol mixture can be
reduced, thereby maintaining the pressure at the first
predetermined value on the polyol mixture. Maintaining the pressure
at the first predetermined value for the first predetermined time
increases a CO.sub.2 content of the polyol mixture.
[0026] An isocyanate is mixed with the polyol mixture to form a
polyurethane reaction mixture. The pressure on the polyurethane
reaction mixture is also optionally maintained at the first
predetermined value for a second predetermined time. Maintaining
the pressure on the polyurethane reaction mixture at the first
predetermined value for the second predetermined time can be done
as described above for the first predetermined time. During the
second predetermined time, when used, the isocyanate and the polyol
mixture in the polyurethane reaction mixture start to react under
the CO.sub.2 pressure at the first predetermined value. In
addition, optionally maintaining the pressure at the first
predetermined value for the second predetermined time can increase
the CO.sub.2 content of the polyurethane reaction mixture to a
value of at least 20 weight percent based (up to the saturation
value) on the total weight of the polyol mixture after the first
predetermined time.
[0027] After the second predetermined time (when used), the
pressure on the polyurethane reaction mixture is increased from the
first predetermined value to a second predetermined value greater
than the first predetermined value. The changes in pressure from
the first predetermined value to a second predetermined value can
be done in a stepwise fashion or in a rate controlled fashion over
a predetermined amount of time (e.g., having a ramp or a curve
pressure change profile). Increasing the pressure on the
polyurethane reaction mixture from the first predetermined value to
the second predetermined value can be done as described above for
the first predetermined time. So, for example, CO.sub.2 can be
supplied to a vessel (e.g., pumped into the vessel) containing the
polyurethane reaction mixture in order to increase the pressure
from the first predetermined value to the second predetermined
value. Alternatively, the volume of a head-space containing the
CO.sub.2 above the polyurethane reaction mixture can be reduced,
thereby increasing the pressure from the first predetermined value
to the second predetermined value.
[0028] The increase in pressure from the first predetermined value
to the second predetermined value starts the second stage of the
two-stage CO.sub.2 pressurization process. During this second stage
of the two-stage CO.sub.2 pressurization process the isocyanate
continues to react with the polyol mixture in the polyurethane
reaction mixture under the CO.sub.2 pressurization at the second
predetermined value for a third predetermined time, where the third
predetermined time is less than 30 minutes. After the third
predetermined time the polyurethane reaction mixture is released at
a predetermined depressurization rate from the pressure to prepare
the rigid PU foam.
[0029] Compared with conventional PU foaming process, a one stage
(with no second stage of the CO.sub.2 pressurization process)
supercritical CO.sub.2 foaming process can reduce the cell size,
but the porosity is less than 80% and the cell size displays a
bi-modal distribution. However, by utilizing the two-stage CO.sub.2
pressurization process of the present disclosure, rigid PU foams
with a number average cell size of no greater than 10 .mu.m and
porosity no less than 85% can successfully be produced. It is also
possible, but less preferable, to produce rigid PU foams with
number average cell sizes of greater than 10 .mu.m and/or with a
porosity of less than 90%. For example, the rigid PU foam of the
present disclosure can be formed with a porosity of no less than
80%. Alternatively, the rigid PU foam of the present disclosure can
be formed with a porosity of no less than 70%.
[0030] The rigid PU foam formed in the two-stage CO.sub.2
pressurization process can also have a crosslink density from 1.0
to 3.0 and a weight average molecular weight (Mw) per cross-link
from 300 to 900. In a preferred embodiment, the rigid PU foam of
the present disclosure has a Mw per cross-link from 400 to 900. In
a preferred embodiment, the rigid PU foam of the present disclosure
has a crosslink density from 1.15 to 3.0. In another preferred
embodiment, the rigid PU foam of the present disclosure has a
crosslink density from and 1.5 to 2.5. The crosslink density has
been discovered to have a significant influence on the number
average cell size of the rigid PU foam. For example, when the
crosslink density of the rigid PU foam goes from 2.98 to 1.76 the
number average cell size of the rigid PU foam goes from 40 .mu.m to
5-8 .mu.m. As such, the number average cell size can be effectively
reduced by changing crosslink density of the rigid PU foam.
[0031] Preferably, the rigid PU foam formed in this two-stage
CO.sub.2 pressurization process also has a porosity of no less than
85 percent. It is also possible to produce a rigid PU foam formed
in the two-stage CO.sub.2 pressurization process having a porosity
of less than 90 percent, if desired. According to some embodiments,
the rigid PU foam can have a volume percentage of closed cells of
no greater than 35 percent based on all the cells in the rigid PU
foam. The rigid PU foam can also have a percentage of open cells
that can be tuned from less than 35 percent (%) to greater than 95%
based on all the cells in the rigid PU foam. So, the rigid PU foam
of the present disclosure can have an open cell volume of at least
35% based on all the cells in the rigid PU foam. Preferably, the
rigid PU foam of the present disclosure can have an open cell
volume content from 35% to 95% based on all the cells in the rigid
PU foam. These percentage values can be determined using ASTM
D2856, as stated above.
[0032] The method for preparing the rigid PU foam of the present
disclosure can be performed in a batch process using a single
vessel. Alternatively, the method for preparing the rigid PU foam
of the present disclosure can be performed in two or more vessels
using a batch, a semi-batch or a continuous process. For example,
in a process that uses a single vessel (e.g., in a batch process)
the first stage of the two-stage CO.sub.2 pressurization process
can include using CO.sub.2 to provide a pressure at a first
predetermined value on the polyol mixture in the vessel. In this
first stage, if a gaseous environment is present above the polyol
mixture in the vessel (e.g., a headspace is present) it can be
purged with CO.sub.2 prior to using the CO.sub.2 to provide the
pressure at the first predetermined value on the polyol mixture.
Purging with CO.sub.2 can help to remove water vapor, oxygen and
other gases from the headspace of the vessel. The CO.sub.2 used to
provide the pressure at the first predetermined value on the polyol
mixture in the vessel can be in either a subcritical state or a
supercritical state, as discussed herein. The pressure at the first
predetermined value is maintained inside the vessel, as discussed
herein (e.g., using CO.sub.2 in either a subcritical state or a
supercritical state) for the first predetermined time to increase
the CO.sub.2 content of the polyol mixture.
[0033] The amount of CO.sub.2 dissolved into the polyol mixture is
calculated by modeling and it is used to estimate the required time
to obtain a certain degree of CO.sub.2 saturation in the polyol
mixture for given temperature and pressure conditions. In other
words, the CO.sub.2 dissolved into the polyol of the polyol mixture
can be estimated from modeling software, which in turn can provide
estimates for the required time at a given temperature and pressure
of CO.sub.2 to obtain the desired degree of CO.sub.2 saturation in
the polyol mixture. The exact amount of time for the first
predetermined time can depend upon the specific equipment used and
is strongly dependent on the contact area between the liquid phase
of the polyol mixture and the phase of the CO.sub.2 and the mixing
equipment, if any, that is used. Preferably, the first
predetermined time is keep to a minimum in order to improve
production rates. For example, the first predetermined time can
preferably be from 30 seconds (s) to 300 s. It is appreciated,
however, that values for the first predetermined time can be
shorter than 30 s or longer than 300 s. For example, it might be
possible to hold the polyol mixture under the pressure at the first
predetermined value for hours or even days, if desired, without any
foreseeable issues to the method for preparing the rigid PU
foam.
[0034] One goal in providing the pressure at the first
predetermined value is to dissolve CO.sub.2 into the polyol
mixture. Dissolving CO.sub.2 in the polyol mixture helps to modify
the reaction kinetics of the polyurethane reaction once the
isocyanate is added to the polyol mixture. Preferably, the amount
of CO.sub.2 present in the polyol mixture is at full saturation for
the given temperature and pressure. In this way, a polyol mixture
that has a saturated amount of CO.sub.2 can be formed and stored
for mixing with the isocyanate, as discussed herein. Preferably,
optionally maintaining the pressure at the first predetermined
value for the second predetermined time can increase a CO.sub.2
content of the polyurethane reaction mixture to a value of at least
20 weight percent based on the total weight of the polyol mixture
after the first predetermined time.
[0035] The temperature and the pressure of the polyol mixture and
of the CO.sub.2 to provide the pressure at the first predetermined
value on the polyol mixture and for maintaining the pressure at the
first predetermined value for the first predetermined time (the
first stage of the two-stage CO.sub.2 pressurization process) is
sufficient to maintain the CO.sub.2 in either a subcritical state
or a supercritical state. For example, the first predetermined
value can be from 5 megapascal (MPa) to 10 MPa at a temperature of
40 degrees Celsius (.degree. C.) to 80.degree. C. This range of
pressures and temperatures allows for CO.sub.2 in either the
subcritical state or the supercritical state. For example, for
temperatures of 40 degrees .degree. C. to 80.degree. C. the
CO.sub.2 will be in a supercritical state for the first
predetermined value for the pressures of at least 7.29 MPa to 10
MPa. For temperatures of 40.degree. C. to 80.degree. C. the
CO.sub.2 will be in a subcritical state for the first predetermined
value for the pressures of 5 MPa to less than 7.29 MPa. Preferably,
the CO.sub.2 used to provide the pressure at the first
predetermined value is in a supercritical state. In addition to
these preferred pressures and temperatures for the CO.sub.2 it is
also possible that the CO.sub.2 used to provide the pressure at the
first predetermined value can have a temperature in a range from at
least 31.1.degree. C. to 100.degree. C. For this temperature range
(31.1.degree. C. to 100.degree. C.), the CO.sub.2 will be in a
supercritical state at a first predetermined value for the pressure
of at least 7.29 MPa.
[0036] The temperature of the polyol mixture at the first stage of
the two-stage CO.sub.2 pressurization process can influence the
reaction rate of the polyol and the isocyanate in the polyurethane
reaction mixture during the second stage of the two-stage CO.sub.2
pressurization process. If the temperature of the polyol mixture
during the first stage is too high, the polyol mixture will have to
be cooled prior to it being mixed with the isocyanate in order to
manage the reaction kinetics. Cooling the polyol mixture prior to
adding the isocyanate is possible, but would shift the
polyol-CO.sub.2 equilibrium established during the first stage of
the method and it would add significant additional complexity. It
is thus preferred to carry out the first stage of the two-stage
CO.sub.2 pressurization process at a temperature lower than or
equal to that of the second stage of the two-stage CO.sub.2
pressurization process.
[0037] As discussed herein, using carbon dioxide to provide a
pressure at the first predetermined value on the polyol mixture
during the first stage of the two-stage CO.sub.2 pressurization
process helps to build up the initial CO.sub.2 concentration in the
polyol mixture. The CO.sub.2 concentration in the polyol mixture in
turn helps to slow down (or decrease) the reaction rate of the
polyol and the isocyanate, so that in the second stage of the
two-stage CO.sub.2 pressurization process there will be enough time
for more CO.sub.2 to dissolve into the polyurethane reaction
mixture. The choice of the second predetermined value for the
pressure of CO.sub.2 in the second stage of the two-stage CO.sub.2
pressurization process can be influenced by such factors as: the
state of the CO.sub.2 (supercritical or subcritical); the density
difference between the polyol mixture and CO.sub.2 phase (for
mixing); and the initial CO.sub.2 concentration in the polyol
mixture and corresponding reaction rate of the polyol and the
isocyanate. Using these principles, it has been determined that the
CO.sub.2 used to increase the pressure on the polyurethane reaction
mixture from the first predetermined value to the second
predetermined value greater than the first predetermined value (the
second stage of the two-stage CO.sub.2 pressurization process)
should be in a supercritical state. As discussed herein, CO.sub.2
is in a supercritical state at a temperature of at least
31.1.degree. C. and a pressure of at least 7.29 MPa. Preferably,
the second predetermined value for the pressure of the CO.sub.2 is
from greater than 10 MPa to 15 MPa at a temperature of 31.degree.
C. to 80.degree. C.
[0038] The density difference between the polyol in the polyol
mixture and the CO.sub.2 in the reactor during either the first
stage or the second stage of the two-stage CO.sub.2 pressurization
process is also taken into consideration in selecting the
temperature of the polyol mixture and the temperature and pressure
of the CO.sub.2 used during these two stages. For example, one goal
during these stages is to minimize the dissolution of polyol into
the CO.sub.2. The preferred state consists of a large amount of
CO.sub.2 dissolved in the polyol mixture and very little or no
polyol dissolved in the CO.sub.2. Dissolution of the polyol into
the CO.sub.2 becomes easier as the density of the CO.sub.2
increases and approaches the density of the polyol mixture. The
density of CO.sub.2 increases with increasing pressure for a set
temperature. Consequently the pressure of the CO.sub.2 should be
set as high as possible (large driving force for polyol
saturation), but low enough to maintain a sufficient barrier to
polyol dissolution into the CO.sub.2. Because of the change in
density value for CO.sub.2 with pressure above a certain point
(dependent on temperature), it is further preferred that the first
predetermined value for the pressure should not be higher than 8
MPa at 40.degree. C., not higher than 8.9 MPa at 50.degree. C. and
not higher than 9.8 MPa at 60.degree. C. In short, considering the
factors listed above, the most preferable first predetermined value
would be from 7 MPa to 8 MPa at a temperature of 40.degree. C. to
80.degree. C.
[0039] As discussed herein, the isocyanate is mixed with the polyol
mixture to form the polyurethane reaction mixture. For the various
embodiments, mixing the isocyanate with the polyol mixture to form
the polyurethane reaction mixture in the vessel at the first
reaction pressure provides a molar ratio of isocyanate groups to
hydroxyl groups of greater than 1 to 1. For example, mixing the
isocyanate with the polyol mixture to form the polyurethane
reaction mixture in the vessel at the first reaction pressure can
provide a molar ratio of isocyanate groups to hydroxyl groups of
greater than 1 to 5.
[0040] For the present disclosure, a mixing time of 90 seconds is
sufficient to achieve adequate mixing of the polyol mixture and the
isocyanate. The first reaction pressure of CO.sub.2 is maintained
in the vessel during the mixing of the isocyanate. The first
reaction pressure of the CO.sub.2 in the vessel containing the
isocyanate and the polyol mixture is optionally maintained for a
second predetermined time during which the isocyanate and the
polyol mixture can react under the first stage CO.sub.2 pressure.
The second predetermined time allows for reaction between the
polyol and isocyanate components to increase the molecular weight
of the mixture, the degree of crosslinking in the growing polymer
network of the polyurethane reaction mixture and to build viscosity
of the polyurethane reaction mixture. The second predetermined time
also helps to prevent the dissolution of the polyurethane reaction
mixture (e.g., polymer, isocyanate, polyol) into the CO.sub.2 phase
during the next processing step. Preferably, the second
predetermined time is from 30 to 300 seconds.
[0041] After the second predetermined time (if used), the pressure
in the vessel is increased, as discussed herein, from the first
reaction pressure to a second reaction pressure greater than the
first reaction pressure. This second reaction pressure helps to
determine the density of the rigid PU foam and can be adjusted to
achieve the desired density. A lower pressure at this stage will
result in a rigid PU foam with higher density (e.g., 350
kg/m.sup.3) and a higher pressure in a foam with a lower density
(e.g., 110 kg/m.sup.3).
[0042] The isocyanate reacts with the polyol mixture in the vessel
at the second reaction pressure for a third predetermined time. The
third predetermined time needs to be long enough to allow for the
required amount of CO.sub.2 to dissolve into the polyurethane
reaction mixture to achieve the desired final foam density. Similar
to what was discussed for the first step, the length of the third
predetermined time can depend on the mixing conditions, contact
area between phases, density and viscosity differences and the
pressure in the reactor. The third predetermined time needs to be
long enough so that the system builds up sufficiently high
viscosity/crosslinking to give the desired cell size during the
pressure release step. The third predetermined time should be short
enough to prevent the reacting mixture from reaching too high a
viscosity and cross-link density that expansion during the
depressurization step does not lead the desired density.
Preferably, the third predetermined time is less than 30 minutes,
and more preferably less than 780 seconds.
[0043] After the third predetermined time, the polyurethane
reaction mixture at the second reaction pressure in the vessel is
released at a predetermined depressurization rate to form the rigid
PU foam. The predetermined depressurization rate determines the
nucleation energy barrier and number of initial nucleation sites in
forming polymer matrix of the rigid PU foam. The higher
depressurization rate is the lower energy barrier will be and the
more nucleation sites there will be. It is preferable to achieve as
high depressurization rate as possible to promote the nucleation
and produce smaller cell size and higher porosity. Preferably,
releasing the polyurethane reaction mixture at the predetermined
depressurization rate from the pressure after the third
predetermined time to prepare the rigid polyurethane foam is done
at a rate of at least 350 MPa/s. These predetermined
depressurization rates have been discovered to produce the rigid PU
foam of the present disclosure with a number average cell size of
no greater than 10 .mu.m and porosity of no less than 85%.
[0044] Releasing the polyurethane reaction mixture at the
predetermined depressurization rate (foam expansion) can be
controlled through the number of release valves in the system. The
polyurethane reaction mixture can be depressurized inside a
pressure vessel or could be injected into a cavity through an
injection nozzle. For the various embodiments, the polyurethane
reaction mixture can be released into standard atmospheric pressure
(101.3 MPa). Alternatively, the polyurethane reaction mixture can
be released into a pressure different from standard atmospheric
pressure. For example, the polyurethane reaction mixture can be
released into a pressure that is less than atmospheric pressure
(e.g., into a vacuum) or into a pressure that is greater than
atmospheric pressure. It is also possible that the rigid PU foam
can undergo a post foam evacuation process (e.g., applying a vacuum
to the rigid PU foam) in order to obtain a lower thermal
conductivity for the rigid PU foam.
Polyol
[0045] The polyol of the present disclosure can be selected from
the group consisting of a polyether polyol, a polyester polyol or a
combination thereof. The polyol of the present disclosure can also
include two or more of the polyether polyol, the polyester polyol
or a combination thereof. The polyol of the present disclosure
include compounds which contain two or more isocyanate reactive
groups, generally active-hydrogen groups, such as primary and/or
secondary hydroxyl groups (--OH). Other suitable isocyanate
reactive groups include primary or secondary amines, and --SH.
[0046] The polyol(s) used in the polyol mixture may each have a
functionality of at least 2 with an upper limit of 8. As used
herein, the polyol functionality of the polyol is not an average
value, but a discrete value for each polyether polyol. In addition,
each polyol in the polyol mixture can have a hydroxyl number of 50
mg KOH/g to 1200 mg KOH/g. In a further embodiment, each polyol in
the polyol mixture can have a hydroxyl number of 100 mg KOH/g to
800 mg KOH/g. So, the polyol mixture has a number averaged
functionality of at least 2, preferably from 3 to 5, and an average
hydroxyl value of at least 100 mg KOH/g. The hydroxyl number gives
the hydroxyl content of a polyol, and is derived from method of
analysis by acetylating the hydroxyl and titrating the resultant
acid against KOH. The hydroxyl number is the weight of KOH in
milligrams that will neutralize the acid from 1 gram of polyol. The
equivalent weight of KOH is 56.1, hence:
Hydroxyl Number=(56.1.times.1000)/Equivalent Weight
where 1000 is the number of milligrams in one gram of sample.
[0047] Examples of polyether polyols include the following
commercially available compositions sold under the trade designator
VORANOL.TM. RN482 (The Dow Chemical Company), VORANOL.TM. CP260
(The Dow Chemical Company), VORANOL.TM. RA640 (The Dow Chemical
Company), TERCAROL.RTM. 5903 (The Dow Chemical Company),
VORATEC.TM.SD 301 (The Dow Chemical Company).
[0048] Other useful polyether polyols include those obtained by the
alkoxylation of suitable starting molecules with an alkylene oxide,
such as ethylene, propylene, butylene oxide, or a mixture thereof.
Examples of initiator molecules include water, ammonia, aniline or
polyhydric alcohols such as dihydric alcohols and alkane polyols
such as ethylene glycol, propylene glycol, hexamethylene diol,
glycerol, trimethylol propane or trimethylol ethane, or the low
molecular weight alcohols containing ether groups such as
diethylene glycol, dipropylene glycol or tripropylene glycol. Other
initiators include pentaerythritol, xylitol, arabitol, sorbitol,
sucrose, mannitol, bisphenol A and the like. Other initiators
include linear and cyclic amine compounds which may also contain a
tertiary amine, such as ethanoldiamine, triethanolamine, and
various isomers of toluene diamine, methyldiphenylamine,
aminoethylpiperazine, ethylenediamine, N-methyl-1,2-ethanediamine,
N-methyl-1,3-propanediamine, N.sub.5N-dimethyl-1,3-diaminopropane,
N,N-dimethylethanolamine, 3,3-diamino-N-methylpropylamine,
N,N-dimethyldipropylenetriamine, aminopropyl-imidazole and mixtures
thereof.
[0049] As provided herein, the polyether polyol can be a
sucrose-initiated or a sorbitol-initiated polyether polyol. For
example, the polyether polyol can be selected from the group
consisting of a sucrose/glycerine-initiated polyether polyol, a
sorbitol propoxylated polyol or a combination thereof. Sucrose may
be obtained from sugar cane or sugar beets, honey, sorghum, sugar
maple, fruit, and the like. Means of extraction, separation, and
preparation of the sucrose component vary depending upon the
source, but are known and practiced on a commercial scale by those
skilled in the art. Sorbitol may be obtained via the hydrogenation
of D-glucose over a suitable hydrogenation catalyst. Fixed beds and
similar types of equipment are especially useful for this reaction.
Suitable catalysts may include, for example, Raney.TM.
(Grace-Davison) catalysts, such as employed in Wen, Jian-Ping, et.
al., "Preparation of sorbitol from D-glucose hydrogenation in
gas-liquid-solid three-phase flow airlift loop reactor," The
Journal of Chemical Technology and Biotechnology, vol. 4, pp.
403-406 (Wiley Interscience, 2004), incorporated herein by
reference in its entirety. Nickel-aluminum and ruthenium-carbon
catalysts are just two of the many possible catalysts.
[0050] The polyol mixture can also include apolyester polyol, which
is obtained by the condensation of appropriate proportions of
glycols and higher functionality polyols with polycarboxylic acids.
Examples of dicarboxylic acids are succinic acid, glutaric acid,
adipic acid, suberic acid, azelaic acid, sebacic acid,
decanedicarboxylic acid, malonic acid, dodecanedicarboxylic acid,
maleic acid, aromatic dicarboxylic acids, and the like. Examples of
dihydric and polyhydric alcohols include ethanediol, diethylene
glycol, triethylene glycol, 1,2- and 1,3-propanediol, dipropylene
glycol, 1,4-butanediol and other butanediols, 1,5-pentanediol and
other pentanediols, and the like. A specific example of a polyester
polyol is STEPANPOL.RTM. 3152, which is based on phtalic
anhydride.
[0051] The polyol mixture of the present disclosure can include 50
weight percent (wt. %) to 99 wt. % of polyol, where the wt. % is
based on a total weight of the polyol mixture. Combinations of more
than one of each type of polyol (e.g., polyether polyol and
polyester polyol) as discussed herein may also be selected,
provided their combined percentages in the polyol mixture as a
whole comply with the stated ranges.
Catalyst
[0052] The catalyst of the present disclosure can be selected from
the group consisting of tertiary amines, tin and bismuth compounds,
alkali metal and alkaline earth metal carboxylates, quaternary
ammonium salts, s-hexahydrotriazines and tris(dialkylaminomethyl)
phenols or a combination thereof. Examples of such catalysts
include, but are not limited to, trimethylamine; triethylamine;
dimethylethanolamine; N-methylmorpholine; N-ethylmorpholine;
N,N-dimethylbenzylamine; N,N-dimethylethanolamine;
N,N,N',N'-tetramethyl-1,4-butanediamine; N,N-dimethylpiperazine;
1,4-diazobicyclo-2,2,2-octane; bis(dimethylaminoethyl)ether;
bis(2-dimethylaminoethyl) ether;
morpholine,4,4'-(oxydi-2,1-ethanediyl)bis; triethylenediamine;
pentamethyl diethylene triamine; dimethyl cyclohexyl amine;
N-acetyl N,N-dimethyl amine; N-coco-morpholine; N,N-dimethyl
aminomethyl N-methyl ethanol amine; N, N,
N'-trimethyl-N'-hydroxyethyl bis(aminoethyl) ether;
N,N-bis(3-dimethylaminopropyl)N-isopropanolamine;
N,N,N,N,N-Pentanmethyldiethylenetriamine;
N,N-Dimethylcyclohexylamine; diethylene glycol, potassium acetate;
Dimethylaminopropyl-hexahydrotriazine,N,N',N''; (N,N-dimethyl)
amino-ethoxy ethanol; N,N,N',N'-tetramethyl hexane diamine;
1,8-diazabicyclo-5,4,0-undecene-7, N,N-dimorpholinodiethyl ether;
N-methyl imidazole; dimethyl aminopropyl dipropanolamine;
bis(dimethylaminopropyl)amino-2-propanol; tetramethylamino bis
(propylamine); (dimethyl(aminoethoxyethyl))((dimethyl
amine)ethyl)ether; tris(dimethylamino propyl) amine; dicyclohexyl
methyl amine; bis(N,N-dimethyl-3-aminopropyl) amine; 1,2-ethylene
piperidine and methyl-hydroxyethyl piperazine. In addition to or
instead of the tertiary amine catalyst mentioned before. Of
particular interest among these are tin carboxylates and
tetravalent tin compounds. Examples of these include stannous
octoate, dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin
dimercaptide, dialkyl tin dialkylmercapto acids, dibutyl tin oxide,
dimethyl tin dimercaptide, dimethyl tin diisooctylmercaptoacetate,
and the like.
[0053] The polyol mixture of the present disclosure can include
0.003 weight percent (wt. %) to 10 wt. % of the catalyst, where the
wt. % is based on a total weight of the polyol mixture.
Combinations of more than one of each type of catalyst as discussed
herein may also be selected, provided their combined percentages in
the polyol mixture as a whole comply with the stated ranges.
[0054] It is also possible that the catalyst could take the form of
a self-catalytic polyol, as are known.
Surfactant
[0055] Surfactants in conventional polyurethane foaming processes
help to decrease the interfacial tension and improve the
compatibility of the raw materials, improve the formation and
stability of nucleation sites, and help to improve the stability of
the growing cells of the expanding foam. For the present
disclosure, the surfactant is also chosen to help in stabilizing
the interface between the CO.sub.2 and the polyol during the
two-stage foaming process of the present disclosure. Helping to
stabilize the CO.sub.2 and polyol interface with the surfactant
helps to decrease the collapse and coalescence of formed bubble
during the depressurization step (the foaming step) of the present
disclosure.
[0056] Based on studies of stabilization times for bubbles formed
from CO.sub.2 and polyol, specific silicone based surfactants have
been identified as being preferred for the polyol mixture. These
silicone based surfactants are characterized by two kinds of
functional chains. One functional chain contains siloxane structure
which is compatible with CO.sub.2. The other functional chain
contains ethoxy or propoxy structure which is compatible with
polyol. Specific examples of such silicone based surfactants
include those sold by Momentive.TM. under the trade designator Niax
Silicone L-6187, Niax Silicone L-6840, Niax Silicone L-6863, Niax
Silicone L-6887, all of which provided stabilization times for
bubbles formed from CO.sub.2 and polyol from 1 hour to about 5
hours at room temperature (23.degree. C.) and standard atmospheric
pressure (101.3 KPa). Another specific and preferred example of a
silicone based surfactant is sold by Maysta.TM. under the trade
designator AK8850, which provided stabilization times for bubbles
formed from CO.sub.2 and polyol for greater than 7 hours at room
temperature (23.degree. C.) and standard atmospheric pressure
(101.3 MPa).
[0057] It is also possible to control the percentage of open-cell
versus closed-cell in the rigid PU foam through the use of
cell-opening surfactants with the silicone based surfactants.
Examples of such cell-opening surfactants include, but are not
limited to those sold by Dupont.TM. and Maysta.TM. under the trade
designator GPL-105, GPL-100, AK-9903 and those sold by
Momentive.TM. under the trade designator Niax Silicone L-6164.
[0058] The polyol mixture of the present disclosure can include 0.5
weight percent (wt. %) to 15 wt. % of surfactant, where the wt. %
is based on a total weight of the polyol mixture. Combinations of
more than one of each type of surfactant as discussed herein may
also be selected, provided their combined percentages in the polyol
mixture as a whole comply with the stated ranges.
[0059] Determining the percentage of open cell is done using
ASTM-D2856
Isocyanate
[0060] In order to prepare the rigid PU foam, react the polyol
mixture with the isocyanate in the presence of a blowing agent
using the two-stage foaming process of the present disclosure.
Preferably the isocyanate is selected from the group consisting of
an aliphatic isocyanate, a cycloaliphatic isocyanate, an aromatic
isocyanate, a polyisocyanate prepolymer or a combination thereof.
These may further include multifunctional aromatic isocyanates.
Also particularly preferred are polyphenyl polymethylene
polyisocyanates (PMDI). For example, isocyanate can be a polymeric
methylene diphenyl diisocyanate. The polymeric form of MDI (p-MDI
or PMDI) is typically 30 percent to 70 percent
diphenylmethanediisocyanate, and the balance is higher
molecular-weight fractions. Examples of preferred commercially
available isocyanates include, those sold under the trade
designator PAPI.TM. 27 and PAPI.TM. 135C both from The Dow Chemical
Company. Other isocyanates useful in the present disclosure include
tolylene diisocyanate (TDI), isophorone diisocyanate (IPDI) and
xylene diisocyanates (XDI), and modifications thereof. These
isocyanates may be used in combinations of two or more types.
[0061] PMDI in any of its forms is a preferred isocyanate for use
with the present disclosure. When used, it preferably has an
equivalent weight of 120 to 150, more preferably from 125 to 145.
The isocyanate can have a functionality from 2.1 to 3. As used
herein, the functionality of the isocyanate is the number of
isocyanate groups [--N.dbd.C.dbd.O] present per molecule of
isocyanate. The viscosity of the isocyanate component is preferably
from 25 to 5,000 centipoise (cP) (0.025 to about 5 Pa*s), but
values from 100 to 1,000 cP at 25.degree. C. (0.1 to 1 Pa*s) are
possible. Similar viscosities are preferred where alternative
isocyanate components are selected.
[0062] The total amount of isocyanate used to prepare the rigid PU
foam of the present disclosure should be sufficient to provide an
isocyanate reaction index of from 0.6 to 5. Preferably the index is
from 0.6 to 1.5. More preferably the index is from 0.7 to 1.2. An
isocyanate reaction index of 100 corresponds to one isocyanate
group per isocyanate reactive hydrogen atom present, such as from
water and the polyol composition. For the mixing of the isocyanate
with the polyol mixture in the vessel at the first reaction
pressure the amount of isocyanate added to the vessel is sufficient
to preferably provide a molar ratio of isocyanate groups to
hydroxyl groups of greater than 1 to 5.
Blowing Agent
[0063] As discussed herein, the primary blowing agent used in the
present disclosure is CO.sub.2 that is introduced into the polyol
mixture during the first and second stages of the two-stage foaming
process of the present disclosure. Use of additional blowing agents
is possible, but not a preferred embodiment.
[0064] The rigid PU foam of the present disclosure can be produced
using the polyol mixture, the isocyanate and the two-stage foaming
process as discussed herein. Batch, semi-continuous and continuous
processes may be used in performing the two-stage foaming process
as discussed herein. For example, for a semi-continuous process the
polyol mixture can be loaded and sealed into a high pressure
vessel. A high pressure mixer (e.g., a static mixer) is coupled to
the high pressure vessel, and the high pressure mixer has an
opening the size of which can be controlled to control the
depressurization rate of the polyurethane reaction mixture emerging
from the high pressure mixer.
[0065] For this example process, supercritical or subcritical
CO.sub.2 is injected into a high pressure vessel to provide a
pressure at the first predetermined value on the polyol mixture.
The pressure of the CO.sub.2 at the first predetermined value is
maintained in the vessel for the first predetermined time to
increase a CO.sub.2 concentration in the polyol mixture. A first
amount of the polyol mixture is then pumped through a high pressure
mixer (e.g., a static mixer) to preload the high pressure mixer and
to maintain proper backpressure in the mixer. Afterward, polyol
mixture and isocyanate are pumped at the desired flow-rate,
pressure and temperature, to a high-pressure mixer. Further
injection of CO.sub.2 may be provided to set the pressure at a
second predetermined value higher than the first predetermined
value (and lower than the pressure in the delivery line of the
pumps). The isocyanate reacts with the polyol mixture in the high
pressure mixer for the third predetermined time (pump rates are set
so that to obtain appropriate residence time). The polyurethane
reaction mixture can then be released through the orifice at the
predetermined depressurization rate.
[0066] Another example process, suitable for discontinuous
production, involves the preparation in a high pressure vessel of a
polyol mixture loaded with CO.sub.2 at a first predetermined
pressure for a first predetermined time, the supply by means of
high pressure pumps of said polyol mixture containing CO.sub.2 and
of isocyanate to a mixing/dispensing apparatus comprising three
chambers, a mixing chamber, a pre-curing chamber and a discharge
chamber. In a preferred set-up the chambers are all provided with a
piston and are constructed each orthogonal to the other. In the
first chamber, the mixing chamber, the polyol mixture and the
isocyanate are mixed by means of high pressure impingement. The
reaction mixture runs to the pre-curing chamber. The piston of the
pre-curing chamber is actuated in such a way to provide the
required volume at controlled pressure during the transfer of the
reaction mixture. Once all of the required reaction mixture has
been transferred, the piston of the mixing chamber closes.
Injection of additional CO.sub.2 can take place during the transfer
from the mixing chamber or alternatively in the pre-curing chamber.
Optionally, the reaction mixture can be held for a second
predetermined time, then pressure is increased to a second
predetermined value and maintained for a third predetermined time.
Once the reaction mixture in the pre-curing chamber is ready for
being poured and/or injected, the piston of the discharge chamber
opens. Proper synchronization of the pistons in the pre-curing
chamber and the discharge chamber allows control of
depressurization rate. The apparatus may advantageously be designed
to allow self-cleaning at the end of pouring.
[0067] The rigid PU foam can be formed into a number of different
shapes and on to or in to a number of different structures. For
example, such structures can include, but are not limited to, rigid
or flexible facing sheet made of foil or another material,
including another layer of similar or dissimilar PU or
polyisocyanurate which is being conveyed, continuously or
discontinuously, along a production line, or directly onto a
conveyor belt. In alternative embodiments the composition for
forming the rigid PU foam may be injected into an open mold or
distributed via lay down equipment into an open mold or simply
deposited at or into a location for which it is destined, i.e., a
pour-in-place application, such as between the interior and
exterior walls of a mold. In the case of deposition on a facing
sheet, a second sheet may be applied on top of the deposited
mixture. In other embodiments, the composition for forming the
rigid PU foam may be injected into a closed mold, with or without
vacuum assistance for cavity-filling. If a mold is employed, it can
be a heated mold.
[0068] The mixture, on reacting, takes the shape of the mold or
adheres to the substrate to produce the rigid PU foam of a
more-or-less predefined structure, which is then allowed to cure in
place or in the mold, either partially or fully. Suitable
conditions for promoting the curing of the composition of the
present disclosure include a temperature of typically from
40.degree. C. to 80.degree. C., preferably from 40.degree. C. to
60.degree. C., and more preferably from 40.degree. C. to 50.degree.
C. Optimum cure conditions will depend upon the particular
components, including catalysts and quantities used in preparing
the composition for forming the rigid PU foam and also the size and
shape of the article manufactured.
[0069] The result can be the rigid PU foam in the form of
slabstock, a molding, a filled cavity, including but not limited to
a pipe or insulated wall or hull structure, a sprayed foam, a
frothed foam, or a continuously- or discontinuously-manufactured
laminate product, including but not limited to a laminate or
laminated product formed with other materials, such as hardboard,
plasterboard, plastics, paper, metal, or a combination thereof. The
rigid PU foam of the present disclosure can be used to form an
insulation panel, where the insulation panel optionally includes a
rigid or flexible facing sheet as discussed herein.
[0070] The composition for forming the rigid PU foam of the present
disclosure can also include other optional additives. Such
additives include, but are not limited to, phosphorous type flame
retardants, chain extenders, silicone surfactants, physical blowing
agents and water, chain extenders, oil, antioxidants, mold release
agents, UV stabilizers, antistatic agents, antimicrobials, flow
aids, processing aids, nucleating agents, pigments, fillers or a
combination thereof. Examples of such phosphorous fire retardants
include, but are not limited to, phosphates and halogen-phosphates
such as triethyl phosphate (TEP) and tris(chloropropyl) phosphate
(TCPP), among others.
[0071] The description hereinabove is intended to be general and is
not intended to be inclusive of all possible embodiments of the
disclosure. Similarly, the examples herein below are provided to be
illustrative only and are not intended to define or limit the
disclosure in any way. Those skilled in the art will be fully aware
that other embodiments, within the scope of the claims, will be
apparent, from consideration of the specification and/or practice
of the disclosure as disclosed herein. Such other embodiments may
include selections of specific components and proportions thereof;
mixing and reaction conditions, vessels, deployment apparatuses,
and protocols; performance and selectivity; identification of
products and by-products; subsequent processing and use thereof;
and the like; and those skilled in the art will recognize that such
may be varied within the scope of the claims appended hereto.
EXAMPLES
Materials
TABLE-US-00001 [0072] TABLE 1 Materials for Examples and
Comparative Examples Component Characteristic Supplier Polyol
VORANOL .TM. F = 6; OH n.sup.o 482, PO based The Dow Chemical RN482
Company (TDCC) (RN482) Polyol VORANOL .TM. F = 4; OH n.sup.o 640,
PO based TDCC RA640 (RN 640) Polyol TERCAROL F = 4; OH n.sup.o 440,
PO based TDCC 5903 (T 5903) Polyol VORATEC .TM. F = 3; OH n.sup.o
160, PO based TDCC SD301 (SD301) Polyol VORANOL .TM. F = 3, OH
n.sup.o 650, PO based TDCC CP260 (CP 260) Polyol SPECFLEX Copolymer
polyol. F = 3, OH n.sup.o 23, Sty TDCC NC 700 and Acrylonitrile
based Polyol STEPANPOL .RTM. F = 2, OH n.sup.o 315 Stepan Company
PS-3152 (PS-3152) Polyol VORANOL .TM. F = 4.9, OH n.sup.o 360, PO
based TDCC RH 360 (RH 360) Polyol VORANOL .TM.CP F = 3, OH n.sup.o
370, PO based TDCC 450 (CP 450) Catalyst POLYCAT .RTM.-5 N,N,N,N,N-
Air product (PC-5) Pentamethyldiethylenetriamine Catalyst POLYCAT
.RTM.-8 N,N-Dimethylcyclohexylamine Air product (PC-8) Catalyst
CURITHANE .RTM.- Diethylene glycol, Potassium acetate TDCC 206
(C-206) Catalyst POLYCAT .RTM.- Dimethylaminopropyl- Air product 41
hexahydrotriazine,N,N',N'' (PC-41) Surfactant AK8850 Silicone
surfactant Dearmate Surfactant L6164 Silicone surfactant Momentive
Cell opener R-501 Silicone surfactant Dearmate Cell opener AK9903
Silicone surfactant Dearmate Isocyanate Papi-27 PMDI TDCC
Isocyanate Papi-135C PMDI TDCC Carbon Dioxide Air product
F--Functionality; OH n.sup.o--hydroxyl number
TABLE-US-00002 TABLE 2 Formulation for Examples1 through 4 and
Comparative Example A Components in Comparative parts by weight
Example 1 Example 2 Example 3 Example A Example 4 Polyol, RN482
64.98 64.98 64.98 0 0 Polyol, RA640 5.09 5.09 5.09 0 0 Polyol,
SD301 25.45 25.45 25.45 95.15 66.6 Polyol, CP260 0 0 0 0 28.54
Surfactant, AK8850 2.04 2.04 2.04 1.9 1.9 Catalyst, PC-41 0.61 0.61
0.61 0.57 0.57 Catalyst, PC-5 0.41 0.41 0.41 0.48 0.48 Catalyst,
PC-8 1.43 1.43 1.43 1.9 1.9 Isocyanate, Papi-27 107 107 107 42.1
80.8 Index = 1.15 Mw per 337 337 337 873 566 crosslink Crosslink
2.97 2.97 2.97 1.15 1.77 Density (1000/Dalton) Reaction Time 8
minutes 9 min 12 min 30 min 10 min 10 sec at (min) 15
Depressurization second (sec) Number average 60 40 70 NA* 8 Cell
Size (micron) Mass 259 342 327 NA* 326 Density (kg/m.sup.3)
*Example 1 foam is not suitable to take measurements.
Foaming Process
[0073] Prepare Examples 1 through 4 and Comparative Example A by
weighing and adding all raw materials of the polyol mixture
(polyol, catalyst and surfactant) for the Example (seen in Table 2)
to a Teflon.RTM. bottle. Mix the content of the Teflon.RTM. bottle
at 3000 rotations per minute (rpm) for 2 minutes at room
temperature (23.degree. C.) and pressure (101 KPa) with a high
speed mixer (INVT SFJ-400, Moderner, China). After mixing remove
the lid of the Teflon.RTM. bottle and allow the contents of the
Teflon.RTM. bottle to equilibrate (release of air bubbles from the
polyol mixture) at room temperature and pressure for one to two
hours.
[0074] Add the polyol mixture from the Teflon.RTM. bottle to a high
pressure reactor and place in a high pressure autoclave that is
located in a temperature controlled water bath. Provide a
sufficient headspace volume above the polyol mixture to allow for
foam expansion. Seal the high pressure autoclave and purge the
atmosphere with carbon dioxide (CO.sub.2) to remove air and water
(H.sub.2O) from the high pressure autoclave. Heat the contents of
the high pressure reactor using the temperature controlled water
bath set to 40.degree. C. Introduce carbon dioxide into the high
pressure autoclave to increase the pressure inside the high
pressure reactor to 7 mega Pascals (MPa). Maintain the pressure and
the temperature inside the high pressure reactor at 7 MPa and
40.degree. C. for 30 minutes to facilitate CO.sub.2 saturation of
the polyol mixture. As discussed above, this first CO.sub.2
saturation step helps to build up the initial CO.sub.2
concentration and slow down (or decrease) the reaction rate of
polyol/isocyanate, so that in following steps, there would be
enough time for more CO.sub.2 dissolved into polyol phase.
[0075] After 30 minutes add the isocyanate (Table 2) and stir the
contents of the reactor for 1 minute. Introduce carbon dioxide into
the high pressure autoclave to increase the pressure inside the
high pressure reactor to 10 MPa. Allow the contents of the high
pressure reactor to react for the reaction time indicated in Table
2 according to different reactivity of formulations. After the
reaction time release the pressure inside the high pressure reactor
within 1 second to atmosphere pressure.
Characterization
Number Average Cell Size Measurement
[0076] Fracture a foam sample utilizing liquid nitrogen. Sputter
coat the fractured face of the foam sample with iridium. Use a
scanning Electron Microscopy (SEM) to obtain images at different
working distances. Obtain the number average cell size through
analysis of the SEM images by using Image-Pro Plus software.
Mass Density Measurement
[0077] Measure mass density of foam samples according to EN ISO 845
or ASTM D792-00, the latter involving weighing polymer foam in
water using a sinker.
Crosslink Density Measurement
[0078] Crosslink Density = 1000 / Mc ##EQU00003## Mc = Wpol + Wiso
Wpol ( Fpol - 2 ) Epol .times. Fpol + Wiso , stoich ( Fiso - 2 )
Eiso .times. Fiso + Wiso , exc ( Fiso - 1 ) Eiso ( Fiso + 1 )
##EQU00003.2##
[0079] Wpol is the weight of the polyol; Wiso,stoich is the weight
of the stoichiometric amount of isocyanate in grams; Wiso,exc is
the weight of the isocyanate exceeding the stoichiometric amount; F
is the numerical average functionality of the components; and E is
the equivalent weight of the components. Mc is the molecular weight
between crosslink.
Open Cell Analysis
[0080] Open cell percentage was measured with the Micromeritics
Accupyc II 1340 based on ASTM D2856.
Discussion of Examples 1 through 4 and Comparative Example A
[0081] Table 2 provides the formulations and measurements of
Examples 1 through 4 and Comparative Example A for the present
disclosure. Examples 1 through 3 are based on commercially
available formulations (without water) and have a cross-link
density of 2.97. The smallest cell size is Example 2 which is
de-pressured at 9 min, and its foam cell size is around 40 micron.
When the de-pressure time was increased to 30 min., the sample
becomes solid in the autoclave and did not foam (Comparative
Example A).
[0082] Example 4 has a cross link density values less than those of
Examples 1 through 3. This adjustment in the cross-link density is
believed to create a smaller number average cell size for the foam
as compared to Examples 1 through 3. The cell size of Example 4
with cross-link density 1.77 is reduced significantly, in the range
of 5 to 8 micron.
CO.sub.2 Solubility in Polyol
[0083] The present disclosure uses CO.sub.2 as a blowing agent. As
such, the desire is to use polyols with a high CO.sub.2 solubility
(the higher the concentration of CO.sub.2 in reactants, the more
nucleation sites and gas resource will be in the bubble nucleation
and growth process). The solubility of CO.sub.2 in different
polyols are determined by magnetic suspension balance (MSB) (see
Sato et al., Solubilities and diffusion coefficients of carbon
dioxide in poly(vinyl acetate) and polystyrene. The Journal of
Supercritical Fluids. 2001; 19(2):187-198; Lei et al., Solubility,
swelling degree and crystallinity of carbon dioxide-polypropylene
system. The Journal of Supercritical Fluids. 2007; 40(3):452-461;
Sato et al., Solubility and Diffusion Coefficient of Carbon Dioxide
in Biodegradable Polymers. Industrial & Engineering Chemistry
Research. 2000; 39(12):4813-4819; and Sato et al., Solubility of
carbon dioxide in PPO and PPO/PS blends. Fluid Phase Equilibria.
2002; 194-197:847-858).
[0084] Table 3 lists the solubility of CO.sub.2 in different
polyols and isocyanate determined from the MSB experiments at
40.degree. C. The solubility of CO.sub.2 increases with increasing
saturation pressure, and the solubility range at 6 MPa lies between
14 wt. % to 34 wt. %, which means the polyol structure (like
chemical backbone, hydroxyl number, molecular weight or
functionality) has a strong impact on the CO.sub.2 solubility.
TABLE-US-00003 TABLE 3 Solubility of CO.sub.2 in Polyols and
Isocyanate at Different CO.sub.2 Pressure. CO.sub.2 saturation
pressure (wt. %) At 2 MPa At 4 MPa At 6 MPa SD301 9.60 26.45 34.20
SPECFLEX NC 700 6.22 14.69 26.48 RN482 3.29 8.60 18.47 PS3152 2.95
7.37 14.08 T5903 3.54 10.51 19.47 PAPI 27 4.13 10.15 19.32 RH360
5.32 16.24 31.97 CP450 5.64 13.83 26.78 CP260 3.99 9.87 18.13
Crosslink Density
[0085] The functionality, equivalent weight, and type of hydroxyl
group of the polyol helps to determine both the polyol reactivity
and the crosslink structure obtained during the reaction. Screening
experiments aiming at determining the appropriate crosslink density
for the process of the present disclosure are shown in Table 4.
[0086] Prepare Examples 5 through 9 by weighing and adding all raw
materials of the polyol mixture (polyol, catalyst and surfactant)
for the Example (Table 4) to a Teflon.RTM. bottle. Process as
discussed above for Examples 1 through 4 and Comparative Example A,
with the following changes. Heat the contents of the high pressure
reactor using the temperature controlled water bath set to
40.degree. C. Introduce carbon dioxide into the high pressure
autoclave to increase the pressure inside the high pressure reactor
to 7 MPa. Maintain the pressure and the temperature inside the high
pressure reactor at 7 MPa and 40.degree. C. for 30 minutes to
facilitate CO.sub.2 saturation of the polyol mixture. After 30
minutes add the isocyanate (Table 4) and stir the contents of the
reactor for 1 minute. Introduce carbon dioxide into the high
pressure autoclave to increase the pressure inside the high
pressure reactor to 10 MPa. Allow the contents of the high pressure
reactor to react for the reaction time indicated in Table 4
according to different reactivity of formulations. After the
reaction time release the pressure inside the high pressure reactor
at a rate of 350 MPa/sec. to atmosphere pressure.
TABLE-US-00004 TABLE 4 Components in parts by weight Example 5
Example 6 Example 7 Example 8 Example 9 Polyol, SD301 66.6 47.57
47.55 9.52 14.28 Polyol CP260 28.54 47.58 38.0 85.63 47.57 Polyol
T5903 0 0 9.5 0 33.3 Surfactant AK8850 1.9 1.9 2.0 1.9 1.9 Catalyst
PC-41 0.57 0.57 0.57 0.57 0.57 Catalyst PC-5 0.48 0.48 0.48 0.48
0.48 Catalyst PC-8 1.9 1.9 1.9 1.9 1.9 Isocyanate Papi-27 80.8
106.6 101 158.2 132.4 Index = 1.15 Mw per crosslink 566 488 486 409
408 Crosslink 1.77 2.05 2.06 2.44 2.45 Density (1000/Dalton)
Reaction Time at 10 min 10 sec 10 min 10 min 10 min 10 min
Depressurization -- -- -- -- -- Number average 8 33 7.5 44 38 Cell
size (.mu.m) Porosity 77% 83% 85% 63% 69%
Compared with conventional PU foaming process, one stage (with no
second stage pressurization process) supercritical CO.sub.2 foaming
process can reduce the cell size, but the porosity is lower than
80%. However, by utilizing the two stage process of the present
disclosure, microcellular PU foams with cell size of approximately
5 microns and porosity of no less than 85% are successfully
produced (e.g., Example 11, below).
Processing Conditions & Examples
[0087] For each of Comparative Examples B through D and Examples 12
and 13 prepare Example 9, as discussed above, with the following
changes. Heat the contents of the high pressure reactor using the
temperature controlled water bath set to 40.degree. C. Introduce
carbon dioxide into the high pressure autoclave to increase the
pressure inside the high pressure reactor as provided in Table 5.
Maintain the temperature and the pressure inside the high pressure
reactor at 40.degree. C. (1.sup.st predetermined pressure) provided
in Table 5. Add the isocyanate and stir the contents of the reactor
for 1 minute. Maintain the reaction pressure for the second
predetermined time provided in Table 5. Introduce carbon dioxide
into the high pressure autoclave to achieve the Saturation pressure
(2.sup.nd predetermined pressure) provided in Table 5. Allow the
contents of the high pressure reactor to react for the overall
reaction time indicated for Example 9 in Table 4. After the
reaction time release the pressure inside the high pressure reactor
as provided in Table 5. A second predetermined time of zero means
either the pressure is kept constant or the pressure is increased
to saturation pressure immediately after the mixing.
TABLE-US-00005 TABLE 5 Reaction Reaction Saturation Pressure
(1.sup.st time (2.sup.nd pressure (2.sup.nd predetermined
predetermined predetermined Depressurization Temperature pressure)
time) pressure rate (.degree. C.) (MPa) (s) (MPa) (MPa/s)
Comparative 40 7 0 7 90 Example B Comparative 40 15 0 15 300
Example C Example D 40 7 0 10 200 Example 10 40 7 30 10 260 Example
11 40 7 30 15 350
Results
Comparative Example B
[0088] With the raw materials of Example 9 listed in Table 4,
following the processing parameters as listed in Table 5, i.e.
pre-saturated with 7 MPa CO.sub.2 for 1 hr, mixing with isocyanate
for 90 s, keep the pressure constant at 7 MPa and release the
pressure at a depressurization rate of 90 MPa/s, PU foams with a
number average cell size of 60 micron, and porosity of 75% are
obtained.
Comparative Example C
[0089] With the raw materials of Example 9 listed in Table 4,
following the processing parameters as listed in Table 5, i.e.
pre-saturated with 15 MPa CO.sub.2 for 1 hr, mixing with isocyanate
for 90 s, keep the pressure constant at 15 MPa and release the
pressure at a depressurization rate of 300 MPa/s, PU foams with a
number average cell size of 40 micron, and porosity of 63% are
obtained.
Example D
[0090] With the raw materials of Example 9 listed in Table 4,
following the processing parameters as listed in Table 5, i.e.
pre-saturated with 7 MPa CO.sub.2 for 1 hr, mixing with isocyanate
for 90 s, immediately increase the pressure to 10 MPa and release
the pressure at a depressurization rate of 200 MPa/s, bimodal cell
size distribution PU foams with a number average cell size of 70
micron and porosity of 85% are obtained.
Example 10
[0091] With the raw materials of Example 9 listed in Table 4,
following the processing parameters as listed in Table 5, i.e.
pre-saturated with 7 MPa CO.sub.2 for 1 hr, mixing with isocyanate
for 90 s, and then reaction at 7 MPa for 30 s, followed by increase
the pressure to 10 MPa and release the pressure at a
depressurization rate of 260 MPa/s, bimodal cell size distribution
PU foams with a number average cell size of 10 .mu.m and porosity
of 87% are obtained.
Example 11
[0092] With the raw materials of Example 9 listed in Table 4,
following the processing parameters as listed in Table 5, i.e.
pre-saturated with 7 MPa CO.sub.2 for 1 hr, mixing with isocyanate
for 90 s, and then reaction at 7 MPa for 30 s, followed by increase
the pressure to 15 MPa and release the pressure at a
depressurization rate of 350 MPa/s, uniform cell size distribution
PU foams with a number average cell size of 4.6 .mu.m, and porosity
of 90.4% are obtained.
CONCLUSION
[0093] From the experiments results delivered from Comparative
Examples B and C, Example D and Examples D, 10 and 11 of Table 5,
it is shown that compared with one-stage foaming process the
two-stage CO.sub.2 pressurization process of the present disclosure
produces rigid PU foams with smaller cell size and high porosity.
While higher saturation pressure, as well as higher
depressurization are also benefit for the generation of
microcellular PU foam with porosity as high as at least 90%.
Open Cell Development
[0094] Use a cell opening surfactant composition to allow cell
opening to occur at the last stage of bubble growth process. This
leads to a high open cell percentage and high porosity of the PU
foam having a cell size of no greater than 10 .mu.m. The cell
opening surfactant composition is a specific ratio of AK8850 and
L6164. AK8850 and L6164 are both silicone surfactants and fit PU
foaming in super critical carbon dioxide system. AK8850 can
stabilize the foam in bubble growth process and L6164 can open
cells at the end of the bubble growth process. When the two
surfactants added with a specific content ratio, a PU foam with
open cell percentage higher than 95%, porosity higher than 86%, and
cell size no greater than 10 .mu.m is obtained. The general
structure of L6164 is as follows:
##STR00001##
Raw Materials and Formulation Information:
TABLE-US-00006 [0095] TABLE 7 Formulation information Example
Comparative Comparative 12 (parts by Example E Example F Example 13
Example 14 Example 15 weight, pbw) (pbw) (pbw) (pbw) (pbw) (pbw)
SD301 47.55 47.07 47.07 47.07 44.15 43.67 CP260 38 37.61 37.61
37.61 35.29 34.90 T5903 9.5 9.4 9.4 9.4 8.82 8.72 PC-41 0.57 0.56
0.56 0.56 0.53 0.52 PC-5 0.48 0.48 0.48 0.48 0.45 0.45 PC-8 1.9
1.88 1.88 1.88 1.76 1.74 R-501 0 1 0 0 0 0 AK9903 0 0 1 0 0 0
AK8850 2 2 2 2 5 3 L6164 0 0 0 1 4 7 Papi- 101 101 101 101 101 101
135C
[0096] Conduct the same two stage foaming process, described above,
for Comparative Examples E and F and Examples 12-15. [0097] 1.
Sample loading: Add polyol mixture into the high pressure
autoclave. Seal the autoclave and purge with CO.sub.2 three times
to remove the air and moisture. [0098] 2. Set the reaction and
pre-saturation temperature at 40.degree. C., increase the CO.sub.2
pressure to 7 MPa and saturation for 1 hr. [0099] 3. Pump
stoichiometric Papi-135C (according to Table 6) into the autoclave
and mixing for 90 s. [0100] 4. Leave the mixture of
polyol/isocyanate reacted for 30 s. [0101] 5. Increase the pressure
to 15 MPa and maintain the pressure constant for 9 min [0102] 6.
Release the pressure at a depressurization rate of 350 MPa/s [0103]
7. The obtained PU foam will be used for characterization.
Results
[0103] [0104] 1. Example 12: With the raw materials as listed in
Table 7, adding only surfactant AK8850, PU foams with a number
average cell size of 4.6 .mu.m, open cell percentage of 29.1%, and
porosity of 90.4% are obtained. [0105] 2. Comparative Example E:
With the raw materials as listed in Table 7, adding the complex of
AK8850 and cell opener R-501, PU foams with a number average cell
size of 52.8 .mu.m, open cell percentage of 84% and porosity of 63%
are obtained. [0106] 3. Comparative Example F: With the raw
materials as listed in Table 7, adding the complex of AK8850 and
cell opener AK9903, bimodal cell size distribution PU foams with
small cell size of 5 .mu.m, big cell size of 25 .mu.m, open cell
percentage of 55.8% and porosity of 81.4% are obtained. [0107] 4.
Example 13: With the raw materials as listed in Table 7, adding the
complex of AK8850 and L6164 with content ratio of 2:1, PU foams
with a number average cell size of 9.7 .mu.m, open cell percentage
of 78.1% and porosity of 82.7% are obtained. [0108] 5. Example 14:
With the raw materials as listed in Table 7, adding the complex of
AK8850 and L6164 with content ratio of 5:4, uniform cell size
distribution PU foams with a number average cell size of 6.1 .mu.m,
open cell percentage of 96.4% and porosity of 86% are obtained.
[0109] 6. Example 15: With the raw materials as listed in Table 7,
adding the complex of AK8850 and L6164 with content ratio of 3:7,
uniform cell size distribution PU foams with a number average cell
size of 6.8 .mu.m, open cell percentage of 92.3% and porosity of
85.8% are obtained.
[0110] When using conventional cell openers in super critical
CO.sub.2 system, the resultant foams show very big cell size, very
low open cell percentage or very low porosity. When using the
complex of AK8850 and L6164 with a specific content ratio
(especially of 5:4), uniform cell size distribution PU foams with
small cell size, high open cell percentage and high porosity are
obtained.
* * * * *